The present invention relates to linear actuator release mechanisms, both in general and as incorporated into a digitally controlled speed control.
Linear actuators, and more particularly digital linear actuators, have been utilized in a wide variety of environments to provide controlled linear reciprocation to a driven element. However, known digital linear actuators "lock-up" in case of a power loss or coil short. Such a lock-up is extremely undesirable because the driven element is maintained in a potentially dangerous position by the nonfunctional actuator. Prior artisans have attempted to alleviate lock-up problems by modifying the linear actuator motor itself. These attempted solutions have been excessively complicated, expensive, and/or ineffective.
An example of an area where this problem has been a major stumbling block is in the area of electronic cruise controls. In attempts to overcome the problems associated with a vacuum type speed control, artisans have attempted to incorporate linear actuators, such as stepper motors, into the throttle-driving mechanism. Generally, a linear actuator includes a housing and a rod extending through the housing and axially reciprocable therein. By coupling one end of the rod to the throttle cable, the throttle can be controlled by axial reciprocation of the rod. Stepper motors have not heretofore been commercially practical because the motors "lock-up" in the event of a coil short or power loss. Specifically, in the case of a "lock-up", the rod is locked in its axial orientation by the nonfunctional driving mechanism. Therefore, when electric power is lost or the motor coil shorts out, the throttle is locked in an open-throttle situation, an extremely dangerous and perhaps uncontrollable condition.
Other problems associated with known vehicle speed controls include causing the vehicle to skid or spin-out on snow, ice, gravel, or other nonresistive driving surfaces. When a vehicle hits an ice patch while operating under the control of the speed control, the wheels tend to spin against the low resistance of the ice for either or both of two reasons. First, the high driving torque applied to the drive wheels causes the wheels to spin against the low coefficient-of-friction surface. Second, when the speed control is not responsive to the drive wheels, as in a motorcycle where the speedometer is driven by the front wheel, the speed control forces the drive wheel to spin faster against the ice in an attempt to accelerate the vehicle to the desired speed. The cruise control in this case opens the vehicle throttle further and further causing the wheels to spin faster, causing instability of the vehicle on the ice. Other conditions where such an undesirable open-throttle situation can occur are where the rear wheel of a motorcycle is off the ground, for example when the motorcycle is tipped over.